A wildlife expert has told how he convinced an African rebel army, which has fought a bloody struggle with the Ugandan government for nearly two decades, to sign up to a conservation project to save one of the world's rarest animals.

Lawrence Anthony, founder of the South African environmental group the Earth Organisation, persuaded the Lord's Resistance Army - the leaders of which are wanted for war crimes by the international criminal court - to join with scientists to protect the northern white rhino, of which only four are thought to remain in the wild. As part of an ongoing peace process, the rebels have pledged not to harm the animals and to tell wildlife experts if they see one.

"I just wondered what on earth could be done to protect the last of this species in the wild," Mr Anthony said, adding: "Desperate times call for desperate measures, I suppose."

Environmentalists feared the worst last year when the LRA took up residence in the Garamba national park, a sprawling and densely forested reserve close to the Ugandan border in the far north-east of the Democratic Republic of Congo. The park is home to the last of the northern white rhino, as well as other rare species including the highly endangered okapi and the pygmy Congo giraffe.

The LRA is notorious for its use of child soldiers and has been accused of numerous atrocities including rapes, mutilations and the mass murder of civilians. Its 19-year fight has left tens of thousands of people dead and an estimated 2 million displaced. Conservation seemed far from its priorities - particularly after its members shot dead 12 of the park's game rangers and then eight Guatemalan UN soldiers sent to the region to keep order this year.

"It was a desperate, impossible situation," Mr Anthony said. "The UN then withdrew entirely from the area and the LRA de facto controlled the park. From that point on the fate of the rhino lay entirely in the hands of this rebel army. That was a conservation disaster. If this species goes extinct they will be the largest land mammal to die out since the woolly mammoth." Unlike the related and relatively abundant sub-species the southern white rhino, the numbers of northern white rhino have failed to recover in recent decades.

Experts feared the LRA, living off meat from the park's animals, would shoot its last rhinos and sell the horns, worth about £20,000 each on the black market, or that with the game rangers too scared to work in the park, the animals would be killed by poachers. "We were closely monitoring the situation, but with precious few solutions available to us. The fate of the rhino appeared to be sealed," Mr Anthony said. "Then we heard that the political wing of the LRA and the Ugandan government were having peace talks in Sudan. We got word that some of the LRA leaders had come out of the Garamba jungle to join the talks and decided to try to talk to them about the rhinos."

With no visa and no invitation, Mr Anthony headed for Juba, southern Sudan, last month. "The talks were taking place at a tented camp in the town. The LRA chairman for the talks, Martin Ojul, was pointed out to me and, during a break in the talks, I simply walked up to him, introduced myself and explained the reason for my visit. His initial response was distrust, covert hostility and no interest."

This is not the first time that Mr Anthony has weighed in in a war on the side of the animals. In April 2003 he was one of the first outsiders to enter Baghdad after the US invasion when he talked his way over the border from Kuwait to rescue species from the ruins of the capital's zoo, the biggest in the Middle East. A book on his exploits will be published next year and a Hollywood film is planned.

The breakthrough with the LRA came the next day when, with the help of an official, Mr Anthony was invited to talk to the rebels about the rhinos. Ignoring warnings of a possible kidnap plot, he met them on the banks of the White Nile river.

"I was surprised that despite the LRA's fearsome reputation some of the delegates were well-educated, articulate and friendly. When I explained there were only four rhinos left in the wild they were genuinely shocked. They thought there were still hundreds of them."

The LRA told Mr Anthony the rhino was the totem of the largest tribe in their home area, giving them a cultural and spiritual affinity with the animal. "They said they did not eat rhino and did not use the horn for medicinal purposes. They said they all grew up in the bush and had strong cultural ties to all wildlife."

When the LRA officials subsequently signed a ceasefire with the government, it included pledges to protect the endangered rhino and to allow the park rangers to resume their work unmolested.

Mr Ojul told agency reporters at the talks: "The statistics we were shown were devastating and shocked us, and so we have given a tacit commitment that we will do whatever possible to live in harmony with the animals. We will act as their curators and do everything possible to see they are not harmed for posterity."

Mr Anthony said: "I was simply blown away. Until this happened the rhinos had no chance whatsoever of surviving. Now they do." He has since received an invitation to visit Joseph Kony, the LRA leader, at his secret headquarters in the reserve and to work in the park under his protection. "We got word that Kony has contacted all of his generals in the park and has told them about this agreement. They said they would allocate soldiers to me for my personal security if I wanted to go into the area and monitor the situation."

Many of the LRA soldiers are now emerging from the park, as agreed under the peace deal. But the future of the rhinos is still far from secure. The game rangers have not yet returned to work, though Mr Anthony said they would be briefed on the ceasefire by an official from the Juba talks this week.

If the estimated four animals can be kept alive (only two have been seen from the air, though scientists say the park may hold twice as many), conservationists hope to breed them with a handful of rhinos in zoos in San Diego and Prague.

"They have a gestation period of 18 months, breed once every three years and have one baby, so this is long-haul stuff," Mr Anthony said. "But if it's accorded the proper importance then it can be done. We've broken new ground with this and I think we have to focus on the positive aspects. The negative aspects are clear; it's an impossible situation. This is a guerrilla army whose leaders are wanted for war crimes and we're doing deals with them."